This invention relates to a rotation sensor device for sensing the angle of rotation and/or a speed of rotation of an electric motor, and more particularly to improvements in a magnetic rotation sensor device utilizing a change in magnetic flux density or reluctance.
Thyristor motors and transistor motors well known as self-controlled synchronous motors generally require a rotation sensor device in order to sense the angular position thereof, which is required for controlling the conduction of thyristors and transistors involved, and the rotational speed thereof, which is required for controlling the rotational speed thereof.
In conventional self-controlled synchronous motors supplied from a variable current source through an associated inverter bridge, the speed sensor such as a tachometer generator or a pulse encoder senses the actual motor-speed signal which is, in turn, compared with a reference motor-speed signal to generate a reference current signal. Then the variable current source controls the sensed actual current supplied to the inverter bridge so it is equal to the reference current signal.
On the other hand, the position sensor senses the actual position signal of the rotating motor and an associated phase control circuit responds to the actual position signal to control the conduction of thyristors or thyristors disposed in the inverter bridge.
Conventional rotation sensor devices such as the speed and position sensors as described above have included a source of light or of magneto-motive force and/or a signal converter circuit for shaping waveforms and so on. Therefore they have had limitations on the external dimensions making it difficult to make them small-sized. As a result, upon installing such a rotation sensor device on an electric motor and particularly on a small-sized electric motor, the resulting motor has been disadvantageous in that its dimensions when it includes a rotational force generation mechanism become large.
Accordingly, it is an object of the present invention to provide a new and improved rotation sensor device which can be made small-sized by using the motor field as a source of magneto-motive force and constructing both a position sensor and a speed sensor in a unitary structure, so that the electric motor provided with the rotation sensor device can be small-sized and yet easy to machine and assemble.